1. Field of the Invention
The present invention relates to an electric actuator, which displaces a displacement member by transmitting a drive force from a driving section to the displacement member through a screw shaft.
2. Description of the Related Art
Heretofore, as an apparatus for transporting a workpiece or the like, an electric actuator has widely been known, in which a feed screw is driven rotatably by a rotary drive force of a rotary drive source, such as a motor or the like, to thereby displace a slider that transports the workpiece.
For example, with the electric actuator 1 disclosed in Japanese Laid-Open Patent Publication No. 10-285867, as shown in FIG. 16, a motor 3 is coupled to an end of a housing 2 formed with a hollow shape, and an operating shaft 4 is inserted reciprocally through the interior of the housing 2. A feed screw shaft 6 is coupled through a coupling 5 to the motor 3, and a nut 7 is screw engaged over the feed screw shaft 6. Additionally, as a result of the nut 7 being accommodated inside the operating shaft 4 and engaged therewith, the feed screw shaft 6 is rotated by driving the motor 3, accompanied by the nut 7 and the operating shaft 4 being moved forward and backward in the axial direction.
However, in the aforementioned conventional technique, the feed screw shaft 6 is supported at one location only by a bearing 8 on one end side where the motor 3 is located. Since the other end side of the feed screw shaft 6 on the side of the housing 2 forms a free end, in the event that the length of the feed screw shaft 6 in the axial direction is long, there is a concern that the other end side will become inclined and off-centered. As a result, vibrations are generated when the feed screw shaft 6 is rotated at high speeds.
Further, although on the one end side of the feed screw shaft 6, a location is provided which is supported by the bearing 8, in the electric actuator 1, the length of the feed screw shaft 6 differs corresponding to the stroke amount (stroke length) of the electric actuator 1 in the axial direction. Along therewith, since the support location by the bearing 8 also differs, in each case, it is necessary to undertake processing corresponding to the stroke amount, which leads to complications. Further, it is necessary to prepare ahead of time various feed screw shafts 6 having different lengths. Consequently, productivity (ease in manufacturing) of the electric actuator 1 including the feed screw shaft 6 thereof is adversely affected and lowered.
Furthermore, upon rotation of the feed screw shaft 6, when the nut 7 is displaced along the axial direction inside the housing 2, there is a concern that the nut 7 will be rotated together with the feed screw shaft 6.